Nitrate ions boost plant growth via protein synthesis

Steps:

• Plants absorb nitrate ions (NO3-) from soil as a nitrogen source.
• Nitrate converts to nitrite, then ammonia, for amino acid production.
• Amino acids link to form proteins, essential for cell growth and enzymes.
• Increased protein synthesis enhances overall plant growth and development.

Why D is correct:

• Nitrate ions provide nitrogen for amino acid synthesis, directly enabling protein production that drives plant growth (per nitrogen cycle in plant nutrition).

Why the others are wrong:

• A: Nitrate has a major positive effect on growth, not none, as nitrogen deficiency limits proteins.
• B: Growth increases with nitrate, but chlorophyll synthesis depends on magnesium, not nitrate.
• C: Nitrate increases growth, not decreases; more chlorophyll relates to iron or magnesium, not nitrate.

Final answer: D